1. Field of the Invention
The present invention relates to a method and a device to measure the mean temperature of components. It can be applied especially to the determining of the junction temperature of microwave electronic components working in continuous wave (CW) mode or in pulse mode.
2. Description of the Prior Art
Radar techniques use, in particular, microwave circuits capable of conveying high power values, such as phase-shifters, limiters or, again, power amplifiers. These amplifiers, which are sometimes calledxe2x80x9csolid-statexe2x80x9d amplifiers, use especially semiconductor-based microwave components such as, for example, class C biased power bipolar transistors. However, the limiters and the phase-shifters most commonly use diodes and, especially, PIN diodes. These different components generally work in radar mode, namely in pulsed operation. In this working mode, the wave is sent by the radar in the form of pulses whose length and repetition period may be fixed or variable in time.
In the microwave components referred to here above such as, for example, the transistors or the diodes, it is important to know the temperature attained by the junction of the component, because this temperature determines the life expectancy of this component. To this end, manufacturers generally provide information on the thermal characteristics of the components and, especially, the thermal resistance Rth which is defined by the following relationship:
Rth=(qjxe2x88x92qs)/Pdxe2x80x83xe2x80x83(1)
where qj is the junction temperature of the component, , qs is the temperature of the component taken at the level of the package and Pd is the power dissipated by the component.
While this feature is valuable for knowing the junction temperature in CW mode, it proves to be insufficient to deal with cases of pulsed operation where it is necessary to introduce the concept of thermal impedance. Indeed, the junction temperature of the component in pulsed mode is closely related to the type of operating microwave frequency used. Taking into account of the progress of the junction temperature is a very important operation, for example when managing and forecasting the life expectancy of a component, especially when making computations on reliability or operational safety, as well as in order to understand special phenomena such as, for example, the phase variation of the microwave signal during successive pulses.
There are methods to determine the junction temperature of the components, especially transistors. These methods make use of current/voltage electrical measurements. In particular, a known current is injected into the transistor and the variation of its base-emitter voltage DVBE is measured. These methods are based on a known property of bipolar transistors according to which, for a given constant current i flowing through the base-emitter junction, any variation in the temperature of the junction causes a variation in the base-emitter voltage VBE according to a known linear relationship. By measuring the variation of this voltage therefore, it is possible, for a given injected current, to determine the variation in junction temperature.
These methods are used solely to determine the temperature when the thermodynamic balance of the component is attained, namely when its temperature is practically stabilized. The value thus obtained corresponds to a maximum value of the junction temperature of the component. Furthermore, the microwave operating frequencies to which the components are subjected during testing generally correspond to fixed pulse widths and repetition periods. Now these measurements give no indication of the precise changes undergone by the junction temperature of the component during the pulses and outside the pulses for a working frequency that starts at the instant t=0 and especially with respect to new modes of radar operation where the pulse widths and the repetition periods are no longer necessarily fixed during one and the same burst of pulses.
The aim of the invention is to overcome the above-mentioned drawbacks, to provide especially for a precise indication of the progress of the mean temperature of the component throughout the phases of the microwave operating frequency both during the pulses and outside the pulses.
To this end, an object of the invention is a method for the measurement of the junction temperature of a component where a sequence of test pulses of increasing width is applied to the component. The peak microwave power of the test pulses represents a state of operation of the component, for example the nominal state of operation. A measurement of junction temperature is performed at the end of each pulse to obtain a curve representing the progress of the junction temperature of the component as a function of time on the basis of the temperature measurement points obtained at the end of each pulse.
The invention also relates to a device for the implementation of the method according to the invention.
The main advantages of the invention are that it can be used to prepare the mean temperature profile of the component as a function of the operating variables of a component, improves the electrothermal models used for the simulation of the circuits, optimizes the electrical circuits, gives a better understanding and better quantification of the temperature-related influences on the electrical characteristics of the circuits, especially with regard to the changes, in time, of their electrical characteristics, and is simple to implement.